1. Field of the Invention
The present invention relates to a solid-state image pickup apparatus, and, more particularly, to a technique for reducing the power consumption of a solid-state image pickup apparatus.
2. Description of the Related Art
Solid-state image pickup apparatuses in which a signal generated by a photoelectric conversion unit is amplified by a plurality of amplification stages have been recently proposed. Japanese Patent Laid-Open No. 2006-109530 discloses a photoelectric conversion apparatus including a first amplification stage in a photoelectric conversion unit and a second amplification stage in a signal storage unit (see, FIG. 1.)
However, since two amplification stages individually have current sources in the photoelectric conversion apparatus, there is room for improvement from the viewpoint of power consumption. When more than two amplification stages are disposed, power consumption is further increased.
In addition, in order to increase a signal reading speed, techniques for reading out signals from a plurality of pixels in parallel and amplifying them have been proposed. When a plurality of reading paths used to process signals in parallel are individually provided with a plurality of amplification stages, power consumption is increased in accordance with the number of reading circuits. For example, in solid-state image pickup apparatuses for copiers, scanners, and single-lens reflex cameras, thousands of reading paths may be disposed in parallel. In this case, power consumption is markedly increased.